The present invention relates to apparatus for measuring viscosity and more particularly to improvements in viscometers utilizing the falling slug principle.
There are various known types of apparatus utilized in the measurement of viscosity and which utilize different principles of operation. Thus there are devices utilizing ultrasonics, vibrating reed, rotary cone, etc., to provide a measure of viscosity.
The present invention is an improved viscometer utilizing the falling slug principle. This principle recognizes that the length of time required for a cylindrical slug to fall a given distance through a fluid in a vertical tube is proportional to the viscosity of the fluid.
As will be seen the improved viscometer of the present invention operates on samples taken from a fluid line and can operate automatically to continuously measure the viscosity of new samples. To provide consistency of measurement, the apparatus first circulates the sample until it attains a temperature within a selected temperature range. In this way all measurements on successive samples will be at the same temperature. Where the temperature of the fluid line is maintained the same, then the circulating step previously noted can be eliminated.
In the present invention the system provides essentially a solid state control system. An electrical signal is provided and stored which is an indication of elapsed time and hence of viscosity. This signal is utilized to provide a visual output such as on a pen recorder. With prior constructions the elapsed time relationship is provided by driving a synchronous motor for the elapsed time with a pen being driven through a suitable gear box. The total travel of the pen is dependent upon the number of revolutions of the motor. To change ranges significantly the gear ratio is required to be changed. In the present electronic system, electrical adjustment means are provided whereby the range, the span and zero can all be set to provide utility for a wide range of viscosities.
In addition the mechanical system provides continuous oscillation between zero and final reading making comparison of successive viscosity readings difficult. In the present invention the last reading is stored and the pen held at that recording position until the next reading modifies the stored reading. In this way the recorded information does not continuously return to zero but provides a series of readings which can be readily compared.
The system also provides an overtime signal in the event a cycle is not completed within a selected time interval which would be indicative of a malfunction. In this event the system is placed and held in a purge phase (to be described).
Therefore it is an object of the present invention to provide an improved viscometer system including solid state controls.
It is another object of the present invention to provide an improved viscometer having electrically adjustable means for modifying calibration, the span, and/or zero set.
It is still another object of the present invention to provide an improved viscometer having means for holding the prior signal and maintaining the recorded read out at the magnitude until the next sample is taken.